The present invention involves horizontal directional drilling systems; more particularly, the present invention involves shallow depth, coiled tubing, horizontal directional drilling systems for the installation of transmission and conveyance linesxe2x80x94to include pipes, tubing, and cable.
Over the past fifteen years, methods for installing underground transmission and conveyance lines have advanced from digging trenches to using horizontal directional drilling techniques in some limited applications. The use of horizontal directional drilling techniques involves drilling horizontal boreholes beneath the earth""s surface using techniques similar to those perfected in the oil and gas exploration industry for drilling deep wells in a high pressure environment.
Horizontal directional drilling is a method for the trenchless installation of underground pipelines. The purpose for the use of horizontal drilling techniques is to install shallow depth transmission and conveyance systems in a minimal or non-pressure environment. Typically, such transmission and conveyance systems are used with various utilities such as electrical power, communications, natural gas, irrigation, petroleum, potable water, storm drains, and sewer service. Shallow depth horizontal directional drilling is accomplished by first drilling a pilot hole in a relatively horizontal plane, exiting the earth, and pulling the transmission or conveyance line; such as pipe or tubing, back through the pilot hole once it has been properly sized.
The drilling equipment used in shallow depth horizontal direction drilling adapts oil field technology for the purpose of drilling horizontal boreholes through earthen materials versus traditional vertical boreholes used in deep wells. However, unlike vertical well drilling, horizontal directional drilling is not performed under the high pressure conditions typically found in deep wells.
All of the known equipment presently in use for shallow depth horizontal directional drilling is based on the use of a rotating segmented pipe string for drilling the borehole. Specifically, the drilling equipment includes either a piston/chain or rack and pinion drive mechanism which pushes or pulls a motor along a length of track. The length of track is slightly longer than the segment of drill pipe being used. During the borehole drilling process, a segment of pipe is loaded onto the track. The segment of pipe is then attached to the drill motor and the previous pipe segment by rotating the drill motor and threading each coupling, or tool joint, together. Once the segments have been threaded and locked together, the drill motor assembly is then thrust forward while rotating all of the pipe segments, at a slight declining angle. The slight declining angle pushes the drill string (pipe) forward into the ground. Once the drill motor has reached the end of the track, the pipe is clamped and the drill motor is counter-rotated to enable disengagement of the drill motor from the drill string. The drill motor is then retracted (pulled back) and another segment of pipe is loaded on the track. This process is continuedxe2x80x94pipe segment by pipe segmentxe2x80x94throughout the entire length of the horizontal borehole that is to be produced.
During the boring (drilling) process the drill motor continually rotates. Accordingly, the entire drill string, including all of the pipe segments, is rotated. The motor is stopped only during times when it is necessary to change the direction of the drillstring through the ground, and add or remove drill pipe segments.
The actual downhole bend or turn of all of the drill pipe segments in the drill string, is accomplished using a bent housing assembly. The bent housing assembly enables the operator to push the drill string to follow the angle of the bent housing assembly. Once the turn of the drill string is completed, the operator engages the drill motor and the drill string is pushed forward while continuing to spin the entire drill string.
Once the initial borehole, or xe2x80x9cpilot hole,xe2x80x9d has been completed, the borehole is typically back reamed. In back reaming, the drilling process is effectively reversed by attaching a larger bit to the drill string and reaming a larger hole while pulling the string back towards the drilling equipment, one pipe segment at a time.
Once the borehole has been back reamed, the drill string is reinserted into the borehole and run to the end. The pipeline to be installed is attached at the exit hole and then pulled into the borehole by the drilling equipment. As with pushing the drill string into the hole, when pulling the drill string, each segment of pipe in the drill string is pulled backxe2x80x94one by onexe2x80x94through the borehole, and detached from the next segment by the drill motor, and subsequently put aside. The drill motor then locks onto the next segment of pipe and pulls the drill string back through the borehole. This segment by segment process continues until the new pipe is fully placed into the ground. All of this work is done without trenching.
The horizontal directional drilling practices described above are parallel to the drilling methods performed in the oil and gas industry. However, today many petroleum contractors are utilizing coiled tubing as a more efficient and diversified means of drilling vertical boreholes for the production of hydrocarbons from deep wells.
The technology of coiled tubing drilling has been used for approximately 30 years. During the past 7-10 years there has been a dramatic increase in the use and applications of coiled tubing in the petroleum sector for use in deep wells. In coiled tubing well drilling, a continuous line of flexible steel pipe is used. The coiled tubing tube is stored on a reel. The primary advantage of using coiled tubing for deep well drilling is the efficiency that is gained from the absence of segmented pipe joints that must be threadably connected, disconnected, and re-connected one from another. In such applications, the leading end of the coiled tubing never exits the earth""s surface.
Historically, segments of drilling pipe were used for drilling and conducting operations inside an oil or gas well, usually several hundreds or thousands of feet under the surface. Each segment of pipe was required to be positioned and attached to the previous pipe segment and then lowered or drilled into the ground. This drilling process, although still highly utilized, is at times laborious and time consuming. With the advent of coiled tubing drilling techniques, drilling contractors were able to supply more efficient and reliable methods of performing many downhole operations in deep wells. With the use of injector heads designed specifically for guiding coiled tubing into a substantially vertical borehole, and various other technologies, operators gained the capacity to continuously feed equipment and fluids into both existing wells and newly drilled wells. When working in deep wells under pressure, the coiled tubing must be able to not only withstand tensile and flexural stresses associated with the drilling process; but also, the internal and external pressures experienced downhole in deep wells.
Many of the same drilling techniques that are utilized when drilling with segmented pipe are also carried out with coiled tubing, but there are clear differences. In a typical coiled tubing well drilling application, the injector head is mounted or suspended in a vertical position above the existing well to be worked over or drilled. The coiled tubing is then guided off a storage reel and over a gooseneck. This gooseneck is utilized to position the coiled tubing for direct insertion into the injector head. The injector head controls the insertion and removal of the coiled tubing from the well. A gooseneck is necessary to provide a means for maximizing the bending radius that the tubing must endure when making the transition from being substantially parallel to the ground, as it leaves the reel, to becoming perpendicular to the ground as it is xe2x80x9cstabbedxe2x80x9d into the injector head and injected substantially vertically down into the well. The coiled tubing drill string is injected or pushed some specific depth into an oil or gas well and the work-over or well drilling operation is performed. Once the drilling of the well is complete, the coiled tubing is retracted, pulled out of the well, and accumulated back onto the storage reel.
Experience in drilling oil and gas wells has shown that coiled tubing typically has a shorter life cycle than straight segmented pipe. This shorter life cycle is due to the bending that coiled tubing must endure as it is reeled on and off the reel and run over the gooseneck. The more bends the coiled tubing is put through, the more fatigued and brittle the coiled tubing becomes, and in turn reduces the number of production cycles available to the user.
Coiled tubing had been predominantly utilized to clean out existing oil and gas wells. However, with advancements in new drilling technologies, the use of coiled tubing has been expanded to well operations such as re-entry and horizontal deviations (kick-offs). Recently, coiled tubing utilization has been expanded into shallow vertical gas well drilling operations by the use of downhole drilling motors. Modern coiled tubing drilling operations are used to drill substantially vertical slim hole wells (wells of smaller than normal diameter), deploy reeled completions, log high angle boreholes, and deploy treatment fluids downhole. The use of coiled tubing in deep directional wells or even in deep horizontal wells (i.e., wells that begin as vertical and then deviate to horizontal) continues to increase at a rapid rate.
The need remains, however, to adapt the coiled tubing drilling techniques used in oil and gas well drilling to shallow depth horizontal drilling for the installation of transmission and conveyance lines.
The present invention includes a system, a method, and an apparatus for utilizing coiled tubing drilling techniques to bore shallow depth, substantially horizontal, boreholes for the installation of transmission and conveyance lines.
The disclosed system, method, and apparatus includes a staging reel from which the coiled tubing is wound and unwound. After exiting the staging reel, the coiled tubing enters a tubing guide system which guides the tubing between the storage reel and the injector head and minimizes the bend radius of unsupported tubing. Controlling the insertion of the coiled tubing in the ground is a coiled tubing injector head. The coiled tubing injector head is adjustably mounted to guide the coiled tubing into the earth at an acute angle. The result is a shallow depth borehole substantially parallel to the earth""s surface. Attached to the leading end of the coiled tubing is a drill motor. Conventional techniques are used to locate and guide the coiled tubing and the drill motor as they pass substantially horizontally through the earth at shallow depths beneath the earth""s surface. The leading end of the coiled tubing exits the earth""s surface. The completed borehole may then be back reamed to enlarge its diameter. Transmission and conveyance lines may follow the back reamer or may be installed after the back reaming operation has been completed. Alternatively, the coiled tubing may be left in the earth to act as a transmission or conveyance line.